Marijuana enthusiasts gather to celebrate the legalization of recreational use of marijuana in Portland, Oregon on Tuesday.
Photograph: Steve Dipaola/Reuters

Oregon became the fourth state in the US to legalize recreational marijuana Wednesday, as revelers cheerfully rang in the new law at midnight.

The Pacific north-west state of just under 4 million people joins four other jurisdictions where marijuana is legal: the states of Alaska, Colorado and Washington and the capital, Washington DC, as advocates are increasingly finding success decriminalizing the substance through ballot initiatives.

However Oregonians, like Alaskans, won’t immediately be able to purchase pot from retail locations. As in the nation’s northernmost state, regulations governing weed sales in Oregon are still being written, with stores expected to open in the next year.

Oregon’s law allows people to grow up to four plants at home for personal use. Smoking marijuana in public is illegal, but Oregonians are also discouraged from calling 911 to report public pot smokers. Users can have up to 8 oz of weed at home, and 1 oz outside of the home.

The implementation of the law comes as advocates are finding increasing success at reducing criminal penalties for possessing marijuana, and introducing ballot measures to legalize the plant. Several ballot initiatives promote decriminalization as a criminal justice reform – a way to limit lopsided enforcement of drug laws against minorities and cut down on unduly harsh prosecutions, advocates say.

“Marijuana prohibition has been a costly failure – to individuals, to communities, and to the state [of Oregon],” said Tamar Todd, marijuana policy director at the Drug Policy Alliance, an organization that advocates against stiff criminal penalties for drug offenses.

“Oregon is taking a smarter, more responsible approach to marijuana that ends the wasteful and racially disproportionate practice of arresting and citing people simply for possessing a small amount of marijuana,” Todd said.